1. Field
One embodiment of the present invention relates to a disk drive using a disk of discrete-track media type as a magnetic recording medium.
2. Description of the Related Art
In the field of disk drives, a representative example of which is a hard disk drive, a disk of discrete-track media (DTM) type has been attracting attention in recent years. (See, for example, Jon. Pat. Appln. KOKAI Publications Nos. 2006-31846, 2006-228348 and 11-45528.) The DTM type disk is also called “patterned media type disk” or “discrete-track recording (DTR) type disk.”
The DT type disk comprises, as basic components, a disk substrate, servo areas provided on the disk substrate, and data areas provided on the disk substrate. Each servo area has magnetic projection-depression patterns, each consisting of projecting magnetic parts and concaved nonmagnetic parts (actually, spaces). The data area has data tracks.
During the manufacturing the DTM disk, it is demanded that the area ratio of magnetic parts (projection-to-depression ratio) be uniform over the entire disk so that a pressure may be uniformly applied to the substrate, particularly while the magnetic layer is being physically processed. To render the area ratio of magnetic parts (projection-to-depression ratio) uniform over the entire disk, the servo patterns provided in the servo areas (servo sectors), each being a magnetic projection-depression pattern, should be uniform, too. The servo patterns are servo data items that are used to achieve the head-positioning control.
Some of the above-identified prior-art publications disclose the technique of providing recording areas on the disk, in which to write servo data. If the disk has such servo-data writing areas, however, the projection-to-depression ratio will change while the disk is being processed, inevitably resulting in non-uniform application of pressure. The above-identified prior-art publications also disclose a technique of generating cylinder codes (address data) in each servo pattern, by a physical process such as etching. However, an extremely fine physical process must be performed in order to generate cylinder codes. This lowers the yield of disk manufacturing. Some of the above-identified prior-art publications indeed disclose the technique of forming magnetic projection-depression patterns on one side of the disk, while forming servo patterns, i.e., flux-reversal patterns, on the other side of the disk. In this case, cylinder codes are recorded on one side of the disk, by means of a physical process. This inevitably reduces the yield of disk manufacturing.